A wide range of vehicles and methods are known for transporting human subjects. Typically, such vehicles rely upon static stability, being designed so as to be stable under all foreseen conditions of placement of their ground-contacting members. Thus, for example, the gravity vector acting on the center of gravity of an automobile passes between the points of ground contact of the automobile's wheels, the suspension keeping all wheels on the ground at all times, and the automobile is thus stable. Alternatively, dynamic stability may be maintained by action of the user, as in the case of a bicycle, or, otherwise, by a control loop, as in the case of the human transporter described in U.S. Pat. No. 5,701,965 and U.S. patent application Ser. No. 08/384,705, filed Feb. 3, 1995, which are herein incorporated by reference.
The balancing vehicles described in these references, however, lack static stability. Referring, for example, to FIG. 1, wherein a prior art personal transporter is shown and designated generally by numeral 18, a subject 10 stands on a support platform 12 and holds a grip 14 on a handle 16 attached to the platform 12, so that the vehicle 18 of this embodiment may be operated in a manner analogous to a scooter. A control loop may be provided so that leaning of the subject results in the application of torque to wheel 20 about axle 22 thereby causing an acceleration of the vehicle. Vehicle 18, however, is statically unstable, and, absent operation of the control loop to maintain dynamic stability, subject 10 will no longer be supported in a standing position and will fall from platform 12. Another prior art balancing vehicle is shown in FIG. 2 and designated generally by numeral 24. Personal vehicle 24 shares the characteristics of vehicle 12 of FIG. 1, namely a support platform 12 for supporting subject 10 and grip 14 on handle 16 attached to platform 12, so that the vehicle 18 of this embodiment may also be operated in a manner analogous to a scooter. FIG. 2 shows that while vehicle 24 may have clusters 26 each having a plurality of wheels 28, vehicle 24 remains statically unstable and, absent operation of a control loop to maintain dynamic stability, subject 10 will no longer be supported in a standing position and will fall from platform 12.
By way of contrast, other prior art vehicles may be statically stable, such as automobiles or the stair-climbing vehicle described in U.S. Pat. No. 4,790,548 (Decelles et al.). These statically stable vehicles, however, lack a balancing capability. They also lack the capability for motion of the vehicle to be governed by leaning of the operator.
In the case of statically unstable balancing vehicles, considerations of operator safety require adoption of special stratagems, such as those described in copending application Ser. Nos. 09/184,488, 08/892,566, and 09/168,551, for the event of failure of certain system components.